Thermo-economic Optimization of Regenerative Organic Rankine Cycle (RORC) Considering Different Working Fluids

In this paper, a Regenerative Organic Rankine Cycle (RORC) for micro-turbine waste heat recovery is modeled and optimized. Refrigerant mass flow rate, Micro- turbine nominal capacity, evaporator pressure, turbine outlet pressure and regenerator efficiency are considered as design parameters. Four refrigerants including R123, R134a, R245fa and R22 are selected and used as working fluids in cycle. Then, NSGA-II (Nondominated Sorting Genetic Algorithm) is used to maximize the thermal efficiency and minimize the total annual cost (including investment cost, fuel cost and environmental cost. The results of the optimal design are a set of optimum solutions, called Pareto front. The optimization results show that the best working fluid is R123 in both of economical and thermo dynamical view point. The optimum result of R123 shows the 3.70%, 18.77%, and 19.74% improvement in thermodynamic efficiency compared with R245fa, R134a, and R22, respectively. The corresponding values for the total annual cost are obtained 6.7%, 10% and 24%, respectively. Generally, it seems that fluids with zero and positive slope of vapor saturation curve have higher thermal efficiency and lower total annual cost. In addition, it is observed that micro-turbine efficiency increased by 12% by the implementation of regenerative organic rankine cycle.